Monitoring system for a conveying device for flat articles, especially wafers

ABSTRACT

The invention relates to a monitoring system for a conveying device for flat articles, especially wafers, which conveying device is provided with a carriage ( 28 ) that is movable along a predetermined path next to a flat article ( 10 ) that is located at a predetermined removal location, the carriage having a receiving device for the accommodation of the flat article ( 10 ), which monitoring system contains a light source ( 50 ) having a light-exit window and a light receiver ( 52 ) having a light-admission window, whereby the light-exit window and the light-admission window are positioned in such a way that a light beam ( 60 ) directed form the light-exit window to the light-admission window is partially covered by the carriage ( 28 ) during its movement through the light beam, and an evaluation unit that is connected to the light receiver and that compares a target signal derived from its movement of the carriage along a target path with an actual signal derived from an actual movement of the carriage, and indicates a deviation.

BACKGROUND OF THE INVENTION

The invention relates to a monitoring system for a conveying device forflat articles, especially wafers.

Wafers are thin disks of silicon, as they are used for the manufactureof integrated circuits, solar cells, etc. Such wafers must be handledextremely carefully in clean rooms, as they are transported, during thecourse of the manufacture of the integrated circuit, the solar cell,etc., from one processing step to a further processing step.

FIG. 3 shows a schematic view of an apparatus for carrying out variousprocessing steps of a wafer.

Two racks 4,6 are disposed in a housing 2 that forms a supply or storagechamber; the racks have receptacles 8 (FIG. 5) that are disposed oneabove the other and in which can be accommodated disks 10.

Via a motor 11 and by means of a device that is not illustrated indetail, the housing 2 can be displaced back and forth on a stationaryrail 12 in the direction of the double arrow 14, so that in one selectedposition, the one rack 4, and in the other selected position, the otherrack 6, is located across from an opening 16 of a housing 18 that hasfurther openings 20 to which the working chambers 22 are connected.

Disposed in a housing 18 is a robot 24 (FIG. 4) that is provided with asupporting arm 26 on which is disposed a carriage 28. The carriage 28has an indentation 30, the base 32 of which is provided with vacuumslots 34 as well as capacitive proximity sensors 36.

To move the supporting arm 26, motors 38 and 40 are provided via whichthe supporting arm 26 is pivoted in a plane of movement that isperpendicular to a central axis of rotation of the robot 24, and viawhich the spacing of the supporting arm from the axis of rotation can bealtered. The carriage 28 can be rigidly connected to the supporting arm26, or can be displaceable on the carrying arm 26 via a non-illustratedfurther drive means.

FIG. 5 shows a perspective front view of the partially cut away orbasically open toward the front housing 2, whereby two chambers arevisible, of which only the left one is provided with the rack 4. Themotor 10 serves for the back and forth movement of the housing 2 uponthe rail 12. As can be seen, the housing 2 is not directly displaceableon the rail 12, but rather is disposed upon a frame element 42 thattogether with the housing 2 is displaceable along the rail 12. Thehousing 2 can be displaced in height relative to the frame element 42via a servo-motor 44, in the direction of the double arrow 46, so thatthe individual receptacles 8, with the wafers 10 accommodated therein,though not illustrated in FIG. 5, can be positioned one after the otherat the same height.

The construction and function of the previously described apparatus,various embodiments of which are offered in commerce by various firms,are known and will therefore not be described in detail.

The basic function is such that pursuant to FIG. 3, the robot 24, in aone time lined-up, horizontal plane, introduces the carriage 28 out ofthe opening 16 and into an oppositely disposed receptacle of the rack 4.With the aid of the servo motor 44, the rack 4 is then lowered slightlyvertically until the proximity sensors 36 register the approach of awafer 10 that is disposed upon a base of a receptacle 8. With a furtherlowering of the rack 4, the wafer 10 comes to rest upon the base 32 ofthe indentation 30, where it is held in place upon activation of thevacuum slots 34. The carriage 28 subsequently moves out of the rack 4into the interior of the housing 18 and through a first one of theopenings 20 into a first one of the working chambers 22, where it isdeposited and processed. The wafer 10 is subsequently picked up by thecarriage 28 and introduced into a next one of the working chambers, etc.until, after passing through the processing steps in the individualworking chambers 22, the wafer is deposited by the carriage 28 in theright rack 6 of FIG. 3, whereby pursuant to FIG. 3 the housing 2 ismoved toward the left. The carriage 28 is subsequently moved out of therack 6, the housing is moved toward the right and the next wafer ispicked up from the rack 4 by first lowering the rack by the height ofone receptacle, so that after the carriage 28 has been introduced intothe next receptacle, and after a subsequent further lowering of the rack4, the next wafer 10 comes to rest on the carriage 28.

The individual openings 16 and 20 of the housing 18 can be sealed offvia vacuum-type slides, so that on the whole it is possible to operateunder vacuum.

A problem that arises when processing with the described apparatus isthat the carriage 28 that is moved by the robot 24 alters its horizontalplane of movement, either due to wear or due to high thermal stresses asit is introduced into the working chambers 22, which are in part underhigh temperature. The vertical distance between the individualreceptacles 18 in the racks 4 and 6 is relatively small, so that alreadya slight deformation or deflection of the carriage out of its targetedpath of movement brings with it the danger that already upon itsintroduction into the rack 4 the carriage contacts a wafer and damagesit, or that the wafer is then no longer satisfactorily deposited uponthe carriage.

It is an object of the invention to provide a remedy for theaforementioned problem.

SUMMARY OF THE INVENTION

This object is realized by a monitoring system pursuant to the mainclaim.

The inventive monitoring system ensures that already slight deviationsof the carriage movement from the targeted path of the carriage aredetected and can be indicated. In this way, expensive damage to thewafers can be avoided.

It is to be understood that the inventive monitoring system forconveying devices pursuant to the main claim is suitable for manydifferent types of flat articles, such as fragile, thin mica plates,thin ceramic plates, loaded printed circuit boards, etc. The inventivemonitoring system is particularly well suited for conveying devices forwafers, the handling of which is subjected to particularly highrequirements.

The dependent claims are directed to advantageous embodiments andfurther developments of the inventive monitoring system.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive monitoring system is explained subsequently with the aidof schematic drawings by way of example and with further details.

The drawings represent:

FIG. 1 a block diagram of the monitoring system,

FIG. 2 curves to explain the functioning of the monitoring system,

FIG. 3 the already described view of a processing apparatus for wafers,

FIG. 4 a perspective view of a robot used in the apparatus of FIG. 3,

FIG. 5 a perspective front view of the apparatus of FIG. 3,

FIG. 6 a perspective view of a modified embodiment of a wafer-processingapparatus, and

FIG. 7 a cross-sectional view through a preparation chamber of theapparatus of FIG. 5.

DESCRIPTION OF PREFERRED EMBODIMENTS

The inventive monitoring system contains a light source 50 and a lightreceiver 52 that is spaced from the light source 50 and is connectedwith a control device 54 to which is connected an indicator 56.

The light source 50 advantageously contains a laser light source, thelight of which is influenced by an optical system in such a way that aparallel light beam 60 (indicated by dashed lines) exits from an exitwindow 58 that is embodied in the form of a vertical slot. The lightbeam 60 enters an admission window 62, of the light receiver 52, that isdisposed across from the exit window 58 and is advantageously embodiedin conformity with the exit slot. The light that enters the admissionwindow 62 is focused on a photo diode, the output signal of which issupplied to the control device 54.

In a manner known per se, the control device 54 contains amicroprocessor and an evaluation unit 64, the function of which will beexplained in detail subsequently.

As can be seen from FIG. 3, the light source 50 is mounted on thestationary housing 18 on one side of the opening 16, and the lightreceiver 52 is mounted on the other side of the opening 16.

FIG. 1 illustrates how movement of the carriage 28, which is movableessentially perpendicular to the plane of the drawing sheet, intersectsor covers the light beam 60. The target plane of movement, in which thecarriage 28 moves during its movement into the rack 4 and out of therack 4, is such that the underside 66 of the carriage 28 intersects thelight beam 60 at a prescribed height, so that a corresponding prescribedheight of the admission window 62 is shaded, and the output signal ofthe light receiver 52 is correspondingly reduced.

In FIG. 2, the curve K represents a measurement curve that representsthe exit signal of the light receiver 52. In the region A there is noobject between the light source 50 and the light receiver 52, so thatthe latter receives the full light intensity, which in the evaluationunit 64 is set to one hundred. If the carriage 28 is moved into thelight beam 60, the intensity of the light falling upon the lightreceiver 52 drops suddenly, depending upon the contour of the carriage,which is recognized by the evaluation unit 64 and sets a counting ortime signal to zero. Depending upon the contour of the carriage 28, thecurve K, as the carriage 28 moves through the light beam 60, assumes acharacteristic path (the brief deviation from the horizontal path in theform of the drop M indicates, for example, a screw that projects fromthe underside 66 of the carriage 28), in order then, depending upon thecontour of the carriage, to again increase until the carriage has movedcompletely through the light beam 60 and in the region A the outputsignal again assumes its original value.

Depending upon the design of the control device 54, the curve K can berecorded at various cycle frequencies and can be evaluated in variousways. In the case of FIG. 2, the region I between the dashed linesrepresents a very narrow precision range within which must lie anaverage value of the output signal that is formed, for example, betweenthe metering positions t₁ and t₂, so that the movement of the carriageis recognized as being in order to a high degree. As long as themeasured value lies between the dot-dashed curves II, the movement ofthe carriage is seen as being still tolerable. Beyond the range II, themovement is seen as not being tolerable, and leads to an indication oferror or malfunction.

In the indicator 56, the indication can be effected directly upon ascreen, in a manner similar to what is shown in FIG. 2, and/or theindication can be effected via diodes, with green diodes indicating “inorder”, yellow diodes indicating “still tolerable”, and red diodesindicating an insufficient precision of movement that requires areadjustment or the like of the carriage.

It is to be understood that a number of other evaluation possibilitiesexist, and that the monitoring apparatus can be installed as anindependent system, or can be integrated into the control system of themotors or the robot and the drive of the housing 2 in a horizontal andvertical direction by supplying, for example, appropriate time markersfrom the control device of the electric motors to the control device 54,etcetera.

It is also to be understood that a drift of the measurement result canbe detected, so that systematic variations can be observed andextrapolated, as a result of which errors can be predicted. Furthermore,it is possible to dispose behind the admission window 62 a diode strip,so that the absolute value of the level of the underside 66 below thelight beam 60 can be detected directly.

Furthermore, the arrangement can also be embodied in such a way that theupper side of the carriage 28 is scanned, so that initially the upperside of the carriage is detected beyond the indentation 30, and then awafer disposed in the indentation 30 is detected, so that with themonitoring of the satisfactory movement of the carriage the satisfactoryposition of the disk and even the satisfactory quality of the diskitself can be monitored.

By calibrating the output signal, with the admission window 62 notcovered, respectively to one hundred, there results an extensiveinsensibility to variations of the light intensity of the light source50 and to contaminations.

FIG. 6 shows a modified embodiment of a wafer-processing apparatus,whereby for functionally similar components the same reference numeralsare used as in FIGS. 3 to 5. With regard to the direction of viewing,the view of FIG. 6 corresponds to a view of the arrangement of FIG. 5 atan angle from behind. The housing 2, which accommodates anon-illustrated rack 4 and 6, contains two hermetically sealable housingcomponents 2 a and 2 b, which contain vacuum chambers in which areaccommodated support means 67 for the magazines or racks 4 and 6 (FIGS.3 and 5). The support means 67 are movable vertically by means ofservo-motors 68. The overall housing 2 is rigidly secured on a frame(not illustrated). In contrast to the embodiment of FIG. 3, where thelight source 50 and the light receiver 52 are disposed on the housing 18that accommodates the robot, with the embodiment of FIG. 6 there isdisposed within each housing portion 2 a and 2 b a light source 50 and alight receiver 52 that are connected via cables 70 to the control device54 (FIG. 1).

The receiving chambers formed in the housing portions 2 a and 2 b areopen in FIG. 6, and can be closed in an airtight manner via slides 72 aand 72 b. With the slides 72 a and 72 b open, racks that are suppliedwith wafers can be inserted or removed at the support means 67.

The geometrical arrangement can be seen from FIG. 7, which represents ahorizontal cross-section through the housing portion 2 a. Visible arethe light source 50, the light receiver 52, the carriage 28, the rack 6and a wafer 10. The arrangement of the light source 50 and of the lightreceiver 52, and the dimensions, are such that the light beam 60(FIG. 1) freely passes through a gap between two receptacles orcompartments that are provided with wafers 10 when the carriage 8 is notdisposed within the rack 6 and the rack is in a predetermined stepposition. The functional sequence of the monitoring system when usingthe embodiment of FIGS. 6 and 7 is as follows:

With the carriage 28 located outside of the housing 2 or one of thehousing portions 2, by actuating the stepping motors 68 the magazinesare respectively in a position in which the light beam passes throughthe gap between two receptacles without being covered, i.e. in the graphof FIG. 2 there results a signal value in the region A, in other words amaximum value of the output signal of the light receiver or receivers52. In the following, the function is described for only one of themagazines, for example the non-illustrated magazine that in FIG. 6 islocated in the right housing portion 2 b. If in the position of thecarriage 28 located outside of the housing portion 2 b the maximum valueof the light intensity is not measured, this indicates an error of thepertaining stepping motor 68 or of its control. The monitoring systemcan be used to control the actuation of the stepping motor 68 byactuating this motor for such a length of time until the maximum lightintensity is achieved. This can occur by trials for an overall, newlyinserted magazine that may be loaded with wafers, so that the magazineimprecisions can be compensated for by always actuating the steppingmotor 68 in such a way that the gap between two receptacle bases isarranged in such a way that the light beam 60 passes completely therethrough. It is to be understood that it is advantageous for the heightdimension of the light beam 60 to be slightly less than the spacingbetween two receptacle bases so that the maximum output signal isensured.

In the predetermined position of the magazine, which is controlled withthe aid of the light beam, the transport arm 26 is now moved into thehousing portion 2 b into the gap between two receptacle bases, i.e. twodisks, the rims of which are accommodated by the receptacle bases,whereby this movement is monitored pursuant to FIG. 2. The monitoringdiffers somewhat from the illustration of FIG. 2 in that the carriage ismoved out of the left region A only in the region B, and not completelythrough the light beam. The rack is subsequently lowered, whereby thelowering is effected by only a certain amount, or, if the proximitysensors 36 (FIG. 4) are provided, the lowering is controlled via theproximity sensors 36. The wafer that rests upon the carriage is thenheld securely in place with the aid of a supply of vacuum to the vacuumslots 34, and is moved out of the housing portion 2 a.

The deposit of the finish-processed wafer in the rack accommodated inthe other housing portion 2 a is effected in a manner analogous to thatexplained in conjunction with FIGS. 3 to 5, whereby the height positionof the rack can, as described, be additionally monitored.

Thus, on the whole, with the inventive monitoring system described byway of example, in the production apparatus a targeted monitoring ispossible at extremely low equipment expense (light emitter and lightreceiver), whereby the monitoring of the vertical movement of the rack,which is provided with the receptacles for accommodating the wafers, andthe movement of the carriage that transports the wafers, utilizes onlyone light receiver and light emitter, whereby the light receivergenerates merely a simple output signal that corresponds to an overallirradiation intensity.

The specification incorporates by reference the disclosure of Germanpriority document 19958 082.0 filed Dec. 2, 1999 and Internationalpriority document PCT/EP00/12103 filed Dec. 1, 2000.

The present invention is, of course, in no way restricted to thespecific disclosure of the specification and drawings, but alsoencompasses any modifications within the scope of the appended claims.

What is claimed is:
 1. A monitoring system for a conveying device forflat articles, wherein said conveying device is provided with a carriagehaving receiving means for accommodating a flat article, said carriagebeing movable along a predetermined path next to a flat article that islocated at a predetermined removal location, said monitoring systemcomprising; a light source having a light-exit window; a light receiverhaving a light-admission window, wherein said light-exit window and saidlight-admission window are positioned such that a light beam directedfrom said light-exit window to said light-admission window can bepartially covered by said carriage during its movement; and anevaluation unit connected to said light receiver, wherein said path ofmovement of said carriage intersects said light beam between saidlight-exit window and said light-admission window and is disposed suchthat said carriage, even during movement along a predetermined targetpath thereof, moves from a position beyond said light beam into aposition within said light beam, and wherein said evaluation unitcompares a target signal, which is derived from movement of saidcarriage along said predetermined target path, with an actual signal,which is derived from an actual movement of said carriage, and indicatesany deviation between such signals.
 2. A monitoring system according toclaim 1, wherein said predetermined path of said carriage extends in aplane, and wherein said light beam is directed parallel to said plane.3. A monitoring system according to claim 1, wherein said light sourceis a laser light source, and wherein said light-exit window and saidlight-admission window are embodied as slots that are directedperpendicular to a plane of said path of movement and between which saidlight beam extends as a parallel light beam.
 4. A monitoring systemaccording to claim 2, wherein said carriage is provided with anunderside that is directed approximately parallel to said plane of saidpath of movement and which, during movement of said carriage along saidtarget path, intersects said light beam.
 5. A monitoring systemaccording to claim 3, wherein said evaluation unit determines at leastone of a target signal and an actual signal by relating an output signalof said light receiver without covering a slot to at least one outputsignal of said light receiver where the slot is covered.
 6. A monitoringsystem according to claim 5, wherein a plurality of output signalsobtained during covering of a slot are determined.
 7. A monitoringsystem according to claim 6, wherein determination of output signalsreceived during covering of a slot is triggered by a reduction of anoutput signal at a beginning of covering of the slot.
 8. A monitoringsystem according to claim 2, wherein a rack is provided that hasreceptacles that are spaced perpendicular to said plane of the movementof said carriage for receiving a plurality of flat articles, whereinsaid rack is movable in stages perpendicular to said path of movement ofsaid carriage such that a flat article accommodated in one of saidreceptacles passes into said predetermined removal location, and whereinsaid light source and said light receiver are disposed such that saidlight beam passes through gaps that are formed between said receptacleswith a predetermined covering by means of a portion of said rack whensaid rack, after removal of a flat article, and movement of saidcarriage with said flat article disposed thereon out, is moved into apredetermined new position, whereby said evaluation unit indicates anerror if the output signal of said light receiver does not correspond tosaid predetermined covering.
 9. A monitoring system according to claim8, wherein in said predetermined new position of said rack said lightbeam is not covered.